Hepatitis C virus (HCV) infects more than 170 million people worldwide, causing acute and chronic hepatitis and hepatocellular carcinoma (HCC)[1]. Notably, increases in HCV cirrhosis have played a major role in the recent rise in HCC, accounting for up to 50% of cases in the United States[2]. With no vaccine available to protect against HCV infection and only a subset of chronically infected patients responding to current treatment options[3], there is an obvious and immediate need for new effective HCV antivirals as well as the HCV experimental model systems that would support advancement in this area. In particular, HCV entry represents a promising multi-faceted opportunity for drug discovery (reviewed in[4]), but a deeper understanding and coherent description of the process is needed to facilitate such endeavors. Thus, our long term goal is to understand the cellular and viral factors that mediate HCV entry in order to identify novel molecular targets amendable to therapeutic intervention and enable the development of transgenic mouse models permissive for HCV entry. Relevant to this long term goal, we recently discovered that the cellular cholesterol uptake receptor Niemann-Pick C1-like 1 (NPC1L1) is required for HCV entry. Based on the observation that exogenous expression of NPC1L1 on the surface of CHO cells results in binding of the cholesterol-enriched HCV virion and the fact that NPC1L1 exhibits restricted tissue distribution and is expressed on human but not mouse hepatocytes, we hypothesize that NPC1L1 is a cholesterol-dependent HCV entry receptor responsible for the restricted human-hepatocyte tropism of HCV entry. As such, we propose to 1) Characterize the interaction between HCV and NPC1L1 during HCV entry by identifying the determinants of the interaction and assessing how and when NPC1L1 functions during the viral entry process; and 2) Elucidate the role of NPC1L1 in HCV tropism by determining if NPC1L1 expression confers HCV permissiveness to non-hepatic and non-human cells. Importantly, these studies will lay the groundwork that will enable a more detailed and specifically focused studies aimed at thoroughly understanding how NPC1L1 participates in HCV entry so that such interactions can be potentially exploited for therapeutic intervention and the development of a mouse model that supports HCV entry.